engine: Added ValidationResult matchers

The matchers can be used for testing that validation result complies
with a given expectation, using JUnit's assertThat syntax.

For example:
To check that validationMethod() returned a valid result:
  assertThat(validationMethod(),isValid());

To check that validationMethod() fails with an error
message VdcBllMessages.EXPECTED_ERROR_MESSAGE:
  assertThat(validationMethod(),
      failsWith(VdcBllMessages.EXPECTED_ERROR_MESSAGE));

Change-Id: I4ed3d5e1e698f5ac00d6a6fe20b855619c35a2ec
Signed-off-by: Mike Kolesnik <mkolesni@redhat.com>